The invention provides for methods to convert vegetable and/or animal oils (e.g. soybean oil) to highly functionalized alcohols in essentially quantitative yields by an ozonolysis process. The functionalized alcohols are useful for further reaction to produce polyesters and polyurethanes. The invention provides a process that is able to utilize renewable resources such as oils and fats derived from plants and animals.
Polyols are very useful for the production of polyurethane-based coatings and foams as well as polyester applications. Soybean oil, which is composed primarily of unsaturated fatty acids, is a potential precursor for the production of polyols by adding hydroxyl functionality to its numerous double bonds. It is desirable that this hydroxyl functionality be primary rather than secondary to achieve enhanced polyol reactivity in the preparation of polyurethanes and polyesters from isocyanates and carboxylic acids, anhydrides, acid chlorides or esters, respectively. One disadvantage of soybean oil that needs a viable solution is the fact that about 16 percent of its fatty acids are saturated and thus not readily amenable to hydroxylation.
One type of soybean oil modification described in the literature uses hydroformylation to add hydrogen and formyl groups across its double bonds, followed by reduction of these formyl groups to hydroxymethyl groups. Whereas this approach does produce primary hydroxyl groups, disadvantages include the fact that expensive transition metal catalysts are needed in both steps and only one hydroxyl group is introduced per original double bond. Monohydroxylation of soybean oil by epoxidation followed by hydrogenation or direct double bond hydration (typically accompanied with undesired triglyceride hydrolysis) results in generation of one secondary hydroxyl group per original double bond. The addition of two hydroxyl groups across soybean oil's double bonds (dihydroxylation) either requires transition metal catalysis or stoichiometric use of expensive reagents such as permanganate while generating secondary rather than primary hydroxyl groups.
The literature discloses the low temperature ozonolysis of alkenes with simple alcohols and boron trifluoride catalyst followed by reflux to produce esters. See J. Neumeister, et al., Angew. Chem. Int. Ed., Vol. 17, p. 939, (1978) and J. L. Sebedio, et al., Chemistry and Physics of Lipids, Vol. 35, p. 21 (1984). A probable mechanism for the low temperature ozonolysis discussed above is shown in FIG. 1. They have shown that a molozonide is generated at relatively low temperatures in the presence of an alcohol and a Bronsted or Lewis acid and that the aldehyde can be captured by conversion to its acetal and the carbonyl oxide can be captured by conversion to an alkoxy hydroperoxide. In the presence of ozone the aldehyde acetal is converted to the corresponding hydrotrioxide at relatively low temperatures. If the reaction temperature is then raised to general reflux temperature, the hydrotrioxide fragments to form an ester by loss of oxygen and one equivalent of original alcohol. At elevated temperatures, and in the presence of an acid such as boron trifluoride, the alkoxy hydroperoxide will eliminate water to also form an ester in essentially quantitative yields. This overall process converts each olefinic carbon to the carbonyl carbon of an ester group so that two ester groups are produced from each double bond.
One broad embodiment of the invention provides for a method for producing an ester. The method includes reacting a biobased oil, oil derivative, or modified oil with ozone and excess alcohol at a temperature between about −80° C. to about 80° C. to produce intermediate products; and refluxing the intermediate products or further reacting at lower than reflux temperature; wherein esters are produced from the intermediate products at double bond sites, and substantially all of the fatty acids are transesterified to esters at the glyceride sites. The esters can be optionally amidified, if desired.
Another broad embodiment of the invention provides a method for producing amides. The method includes amidifying a biobased oil, or oil derivative so that substantially all of the fatty acids are amidified at the glyceride sites; reacting the amidified biobased oil, or oil derivative with ozone and excess alcohol at a temperature between about −80° C. to about 80° C. to produce intermediate products; refluxing the intermediate products or further reacting at lower than reflux temperature, wherein esters are produced from the intermediate products at double bond sites to produce a hybrid ester/amide.
Broadly, the present invention provides for the ozonolysis and transesterification of biobased oils, oil derivatives, or modified oils to generate highly functionalized esters, ester alcohols, amides, and amide alcohols. By biobased oils, we mean vegetable oils or animal fats having at least one triglyceride backbone, wherein at least one fatty acid has at least one double bond. By biobased oil derivatives, we mean derivatives of biobased oils, such as hydroformylated soybean oil, hydrogenated epoxidized soybean oil, and the like wherein fatty acid derivatization occurs along the fatty acid backbone. By biobased modified oils, we mean biobased oils which have been modified by transesterification of the fatty acids at the triglyceride backbone.
Ozonolysis of olefins is typically performed at moderate to elevated temperatures whereby the initially formed molozonide rearranges to the ozonide which is then converted to a variety of products. Although not wishing to be bound by theory, it is presently believed that the mechanism of this rearrangement involves dissociation into an aldehyde and an unstable carbonyl oxide which recombine to form the ozonide. The disclosure herein provides for low temperature ozonolysis of fatty acids that produces an ester alcohol product without any ozonide, or substantially no ozonide as shown in FIG. 2. It has been discovered that if a polyol such as glycerin is used in this process (and in excess) that mainly one hydroxyl group will be used to generate ester functionality and the remaining alcohol groups will remain pendant in generating ester glycerides.
One basic method involves the combined ozonolysis and transesterification of a biobased oil, oil derivative, or modified oil to produce esters. As shown in FIG. 1, if a monoalcohol is used, the process produces an ester. As shown in FIG. 2, if a polyol is used, an ester alcohol is made.
The process typically includes the use of an ozonolysis catalyst. The ozonolysis catalyst is generally a Lewis acid or a Bronsted acid. Suitable catalysts include, but are not limited to, boron trifluoride, boron trichloride, boron tribromide, tin halides (such as tin chlorides), aluminum halides (such as aluminum chlorides), zeolites (solid acid), molecular sieves (solid acid), sulfuric acid, phosphoric acid, boric acid, acetic acid, and hydrohalic acids (such as hydrochloric acid). The ozonolysis catalyst can be a resin-bound acid catalyst, such as SiliaBond propylsulfonic acid, or Amberlite® IR-120 (macroreticular or gellular resins or silica covalently bonded to sulfonic acid or carboxylic acid groups). One advantage of a solid acid or resin-bound acid catalyst is that it can be removed from the reaction mixture by simple filtration.
The process generally takes place at a temperature in a range of about −80° C. to about 80° C., typically about 0° C. to about 40° C., or about 10° C. to about 20° C.
The process can take place in the presence of a solvent, if desired. Suitable solvents include, but are not limited to, ester solvents, ketone solvents, chlorinated solvents, amide solvents, or combinations thereof. Examples of suitable solvents include, but are not limited to, ethyl acetate, acetone, methyl ethyl ketone, chloroform, methylene chloride, and N-methylpyrrolidinone.
When the alcohol is a polyol, an ester alcohol is produced. Suitable polyols include, but are not limited to, glycerin, trimethylolpropane, pentaerythritol, or propylene glycol, alditols such as sorbitol and other aldoses and ketoses such as glucose and fructose.
When the alcohol is a monoalcohol, the process may proceed too slowly to be practical in a commercial process and the extended reaction time can lead to undesired oxidation of the monoalcohol by ozone. Therefore, it may be desirable to include an oxidant. Suitable oxidants include, but are not limited to, hydrogen peroxide, Oxone® (potassium peroxymonosulfate), Caro's acid, or combinations thereof.
The use of a modified oil, which has been transesterified to esters at the fatty acid glyceride sites before reacting with the ozone and excess alcohol, allows the production of hybrid C9 or azelate esters (the major component in the reaction mixture) in which the ester on one end of the azelate diester is different from the ester on the other end. In order to produce a hybrid ester composition, the alcohol used in ozonolysis is different from the alcohol used to transesterify the esters at the fatty acid glyceride sites.
The esters produced by the process can optionally be amidified to form amides. One method of amidifying the esters to form amides is by reacting an amine alcohol with the esters to form the amides. The amidifying process can include heating the ester/amine alcohol mixture, distilling the ester/amine alcohol mixture, and/or refluxing the ester/amine alcohol mixture, in order too drive the reaction to completion. An amidifying catalyst can be used, although this is not necessary if the amine alcohol is ethanolamine, due to its relatively short reaction times, or if the reaction is allowed to proceed for suitable periods of time. Suitable catalysts include, but are not limited to, boron trifluoride, sodium methoxide, sodium iodide, sodium cyanide, or combinations thereof.
Another broad embodiment of the invention provides a method for producing amides. The method includes amidifying a biobased oil, or oil derivative so that substantially all of the fatty acids are amidified at the triglyceride sites, as shown in FIG. 7. The amidified biobased oil, or oil derivative is then reacted with ozone and excess alcohol to produce esters at the double bond sites. This process allows the production of hybrid ester/amides.
The ester in the hybrid ester/amide can optionally be amidified. If a different amine alcohol is used for the initial amidification process from that used in the second amidification process, then C9 or azelaic acid hybrid diamides (the major component in the reaction mixture) will be produced in which the amide functionality on one end of the molecule is different from the amide functionality on the other end.
Ester Polyols
The following section discusses the production of highly functionalized glyceride alcohols (or glyceride polyols) from soybean oil by ozonolysis in the presence of glycerin and boron trifluoride as shown in FIG. 3. Glycerin is a leading ester polyol precursor candidate since it is projected to be produced in high volume as a byproduct in the production of methyl soyate (biodiesel). Other candidate reactant polyols include propylene glycol (a diol), trimethylolpropane (a triol) and pentaerythritol (a tetraol), alditols such as sorbitol and other aldoses and ketoses such as glucose and fructose.
Broadly, ozonolysis of soybean oil is typically performed in the presence of a catalyst, such as catalytic quantities of boron trifluoride (e.g., 0.06-0.25 equivalents), and excess glycerin (e.g. four equivalents of glycerin) (compared to the number of reactive double bond plus triglyceride sites) at about −80° C. to about 80° C. (preferably about 0° C. to about 40° C.) in a solvent such as those disclosed herein.
It is expected that dehydrating agents such as molecular sieves and magnesium sulfate will stabilize the ester product by reducing product ester hydrolysis during the reflux stage based on chemical precedents.
Completion of ozonolysis was indicated by an external potassium iodide/starch test solution, and the reaction mixture was refluxed typically one hour or more in the same reaction vessel. Boron trifluoride was removed by treatment with sodium carbonate, and the resulting ethyl acetate solution was washed with water to remove excess glycerin.
One benefit of using boron trifluoride as the catalyst is that it also functions as an effective transesterification catalyst so that the excess glycerin also undergoes transesterification reactions at the site of original fatty acid triglyceride backbone while partially or completely displacing the original glycerin from the fatty acid. Although not wishing to be bound by theory, it is believed that this transesterification process occurs during the reflux stage following the lower temperature ozonolysis. Other Lewis and Bronsted acids can also function as transesterification catalysts (see the list elsewhere herein).
Combined proton NMR and IR spectroscopy confirmed that the primary processes and products starting with an idealized soybean oil molecule showing the relative proportions of individual fatty acids are mainly 1-monoglycerides as indicated in FIG. 3. However, some 2-monoglycerides and diglycerides are also produced. FIG. 3 illustrates typical reactions for an idealized soybean oil molecule. FIG. 3 also shows that monoglyceride groups become attached to each original olefinic carbon atom and the original fatty acid carboxylic groups are also transesterified primarily to monoglyceride groups to generate a mixture of primarily 1-monoglycerides, 2-monoglycerides and diglycerides. Thus, not only are the unsaturated fatty acid groups multiply derivatized by glycerin, but the 16% saturated fatty acids are also converted primarily to monoglycerides by transesterification at their carboxylic acid sites.
Excess glycerin (four equivalents) was used in order to produce primarily monoglycerides at the double bond sites and minimize formation of diglycerides and triglycerides by further reaction of pendant product alcohol groups with the ozonolysis intermediates. However, diglycerides can still function as polyols since they have available hydroxyl groups. One typical structure for diglycerides is shown below as Formula I.

This follows since the higher the concentration of glycerin, the greater the probability that, once a hydroxyl group of a glycerin molecule (preferentially primary hydroxyl groups) reacts with either the aldehyde or carbonyl oxide intermediates, the remaining hydroxyl groups in that molecule will not also be involved in these type reactions.
1-Monoglycerides have a 1:1 combination of primary and secondary hydroxyl groups for preparation of polyurethanes and polyesters. The combination of more reactive primary hydroxyl groups and less reactive secondary hydroxyl groups may lead to rapid initial cures and fast initial viscosity building followed by a slower final cure. However, when using starting polyols comprised substantially exclusively of primary hydroxyl groups such as trimethylolpropane or pentaerythritol, substantially all pendant hydroxyl groups will necessarily be primary in nature and have about equal initial reactivity.
The theoretical weight for the preparation of soybean oil monoglycerides shown above is about two times the starting weight of soybean oil, and the observed yields were close to this factor. Thus, the materials cost for this transformation is close to the average of the per pound cost of soybean oil and glycerin.
Glyceride alcohols obtained were clear and colorless and had low to moderately low viscosities. When ethyl acetate is used as the solvent, hydroxyl values range from 230 to approximately 350, acid values ranged from about 2 to about 12, and glycerin contents were reduced to <1% with two water washes.
When ester solvents such as ethyl acetate are used, there is a potential for a side reaction in the production of vegetable oil glyceride alcohols (example for soybean oil shown in FIG. 3), or ester alcohols in general, that involves the transesterification of the free hydroxyl groups in these products with the solvent ester to form ester-capped hydroxyl groups. When ethyl acetate is used, acetate esters are formed at the hydroxyl sites, resulting in capping of some hydroxyl groups so that they are no longer available for further reaction to produce foams and coatings. If the amount of ester capping is increased, the hydroxyl value will be decreased, thus providing a means to reduce and adjust hydroxyl values. Ester capping may also be desirable since during purification of polyol products by water washing, the water solubility of the product ester alcohol is correspondingly decreased leading to lower polyol product loss in the aqueous layer.
Several methods are available to control ester capping reactions, and thus the hydroxyl value of the ester alcohol.
One method is shown in FIG. 6, which illustrates an alternate approach to prepare vegetable oil glyceride alcohols, or ester alcohols in general, by reacting (transesterifying) the vegetable oil methyl ester mixture (shown in FIG. 4), or any vegetable oil alkyl ester mixture, with glycerin, or any other polyol such as trimethylolpropane or pentaerythritol, to form the same product composition shown in FIG. 3, or related ester alcohols if esters are not used as solvents in the transesterification step. Also, if esters are used as solvents in transesterifying the mixture of FIG. 4 (alkyl esters) with a polyol, a shorter reaction time would be expected compared to transesterification of the fatty acids at the triglyceride backbone (as shown in FIG. 3), thus leading to decreased ester capping of the hydroxyl groups. This method has merit in its own right, but involves one extra step than the sequence shown in FIG. 3.
Another method of controlling the ester capping in general is to use solvents that are not esters (such as amides such as NMP (1-methyl-2-pyrrolidinone) and DMF (N,N-dimethyl formamide); ketones, or chlorinated solvents) and can not enter into transesterification reactions with the product or reactant hydroxyl groups. Alternatively, “hindered esters” such as alkyl (methyl, ethyl, etc.) pivalates (alkyl 2,2-dimethylpropionates) and alkyl 2-methylpropionates (isobutyrates) can be used. This type of hindered ester should serve well as an alternate recyclable solvent for vegetable oils and glycerin, while its tendency to enter into transesterification reactions (as ethyl acetate does) should be significantly impeded due to steric hindrance. The use of isobutyrates and pivalates provides the good solubilization properties of esters without ester capping to provide maximum hydroxyl value as desired.
Another way to control the ester capping is to vary the reflux time. Increasing the reflux time increases the amount of ester capping if esters are used as ozonolysis solvents.
Ester capping of polyol functionality can also be controlled by first transesterifying the triglyceride backbone, as shown in FIG. 8 and described in Example 2, and then performing ozonolysis, as described in Example 3, resulting in a shorter reaction time when esters are used as solvents.
Water washing of the product in ethyl acetate solutions has been used to remove the excess glycerin. Because of the high hydroxyl content of many of these products, water partitioning leads to extreme loss of ester polyol yield. It is expected that using water containing the appropriate amount of dissolved salt (sodium chloride or others) will lead to reduced product loss currently observed with water washing. Even though not demonstrated, the excess glycerin used presumably can be separated from water washes by simple distillation.
In order to remove the acid catalyst boron trifluoride effectively without water partitioning, basic resins, such as Amberlyst® A-21 and Amberlyst® A-26 (macroreticular or gellular resins of silica covalently bonded to amine groups or quaternary ammonium hydroxide), have been used. The use of these resins may also be beneficial because of potential catalyst recycling by thermal treatment to release boron trifluoride from either resin or by chemical treatment with hydroxide ion. Sodium carbonate has been used to scavenge and also decompose the boron trifluoride catalyst.
The present invention allows the preparation of a unique mixture of components that are all end functionalized with alcohol or polyol groups. Evidence indicates when these mixtures are reacted with polyisocyanates to form polyurethanes, that the resulting mixtures of polyurethanes components plasticize each other so that a very low glass transition temperature for the mixed polyurethane has been measured. This glass transition is about 100° C. lower than expected based solely on hydroxyl values of other biobased polyols, none of which have been transesterified or amidified at the glyceride backbone. Also, the polyols derived from these cleaved fatty acids have lower viscosities and higher molecular mobilities compared to these non-cleaved biobased polyols, leading to more efficient reactions with polyisocyanates and molecular incorporation into the polymer matrix. This effect is manifested in polyurethanes derived from the polyols of the present invention giving significantly lower extractables in comparison to other biobased polyols when extracted with a polar solvent such as N,N-dimethylacetamide.
Amide Alcohols
The following section discusses the production of highly functionalized amide alcohols from soybean oil by ozonolysis in the presence of methanol and boron trifluoride followed by amidification with amine alcohols. Refer now to FIGS. 4 and 5.
Ozonolysis of soybean oil was performed in the presence of catalytic quantities of boron trifluoride (0.25 equivalent with respect to all reactive sites) at 20-40° C. in methanol as the reactive solvent. It is anticipated that significantly lower concentrations of boron trifluoride or other Lewis or Bronsted acids could be used in this ozonolysis step (see the list of catalysts specified elsewhere). Completion of ozonolysis was indicated by an external potassium iodide/starch test solution. This reaction mixture was then typically refluxed typically one hour in the same reaction vessel. As stated previously, in addition to serving as a catalyst in the dehydration of intermediate methoxy hydroperoxides and the conversion of aldehydes to acetals, boron trifluoride also serves as an effective transesterification catalyst to generate a mixture of methyl esters at the original fatty acid ester sites at the triglyceride backbone while displacing glycerin from the triglyceride. It is anticipated that other Lewis and Bronsted acids can be used for this purpose. Thus, not only are all double bond carbon atoms of unsaturated fatty acid groups converted to methyl esters by methanol, but the 16% saturated fatty acids are also converted to methyl esters by transesterification at their carboxylic acid sites. Combined proton NMR and IR spectroscopy and GC analyses indicate that the primary processes and products starting with an idealized soybean oil molecule showing the relative proportions of individual fatty acids are mainly as indicated in FIG. 4.
Amidification of the methyl ester mixture was performed with the amine alcohols diethanolamine, diisopropanolamine, N-methylethanolamine, N-ethylethanolamine, and ethanolamine. These reactions typically used 1.2-1.5 equivalents of amine and were driven to near completion by ambient pressure distillation of the excess methanol solvent and the methanol released during amidification, or just heat under reflux, or at lower temperatures. These amidification reactions were catalyzed by boron trifluoride or sodium methoxide which were removed after this reaction was complete by treatment with the strong base resins Amberlyst A-26® or the strong acid resin Amberlyte® IR-120, respectively. Removal of boron trifluoride was monitored by flame tests on copper wire wherein boron trifluoride gives a green flame. After amidification reactions with amine alcohols, excess amine alcohols were removed by short path distillation using a Kugelrohr short path distillation apparatus at temperatures typically ranging from 70° C. to 125° C. and pressures ranging from 0.02-0.5 Torr.
Combined proton NMR and IR spectroscopy indicate that the primary amidification processes and products starting with the cleaved methyl esters after initial ozonolysis and then reacting with an amine alcohol such as diethanolamine are mainly as indicated below in FIG. 5. Thus, not only are the unsaturated fatty acid groups of soybean oil multiply converted to amide alcohols or amide polyols at their olefinic sites as well as the fatty acid triglyceride sites, but the 16% saturated fatty acids are also converted to amide alcohols or amide polyols at their fatty acid sites.
The boron trifluoride catalyst may be recycled by co-distillation during distillation of excess diethanolamine, due to strong complexation of boron trifluoride with amines.
One problem that has been identified is the oxidation of monoalcohols such as methanol, that is used both as a solvent and reactant, by ozone to oxidized products (such as formic acid, which is further oxidized to formate esters, when methanol is used). Methods that have been evaluated to minimize this problem are listed below:    (1). Perform ozonolysis at decreased temperatures, ranging from about −78° C. (dry ice temperature) to about 20° C.;    (2). Perform ozonolysis reaction with alcohols less prone to oxidation than methanol such as primary alcohols (ethanol, 1-propanol, 1-butanol, etc.), secondary alcohols (2-propanol, 2-hydroxybutane, etc.), or tertiary alcohols, such as tertiary-butanol;    (3). Perform ozonolysis reaction using alternate ozone non-reactive cosolvents (esters, ketones, tertiary amides, ketones, chlorinated solvents) where any monoalcohol used as a reagent is present in much lower concentrations and thus would compete much less effectively for oxidation with ozone.
The boron trifluoride catalyst may be recycled by co-distillation during distillation of excess diethanolamine, due to strong complexation of boron trifluoride with amines.
All examples herein are merely illustrative of typical aspects of the invention and are not meant to limit the invention in any way.